1Anthropology, University of Pittsburgh, 2Human Evolutionary Biology, Harvard University, 3Molecular and Cellular Biology, Harvard University, 4Anthropology, Yale University
April 16, 2020 32, Platinum Ballroom
Testosterone is integral to men’s life history strategies, although separate adaptive mechanisms are proposed for determining testosterone variation: H1) behavioral investment in mating effort versus paternal involvement; H2) energetic regulation of somatic investment toward mating effort; and H3) physiological support of physical activity. Here, we report hormone data from Western Qom men, a rural indigenous population of transitional foragers. The wet season, or Wo´e, for Western Qom is characterized by increased food availability, decreased workload, and a culturally-ascribed time of mateship formation. This contrasts with the dry season, nakabia´Ga, with greater work demands and nutritional constraint. Anthropometric, demographic, and life history data along with saliva samples were collected during Wo´e and nakabia´Ga for 47 Qom men, 17-67 years. We examine seasonal variation in reproductive effort, testosterone levels, and workload to parse competing predictions. Morning and evening testosterone were significantly higher, 33% and 40%, respectively, during Wo´e, a period when nutritional constraint and workload is attenuated but mating effort intensified. And although seasonal energy availability was increased generally across the study sample, testosterone elevation was more specific and significantly higher among single/childless men than pair-bonded fathers for morning testosterone, 89% versus 19% increase, but with no statistical difference in evening values. Moreover, testosterone elevation was age-dependent only to the extent that younger ages had more single/childless men; older single/childless men exhibited testosterone seasonality analogous to their younger single/childless counterparts. Among Western Qom men, the overall patterned variation of fluctuating testosterone is most consistent with behavioral partitioning of mating and parenting effort.